68Ga-Prostate-Specific Membrane Antigen-Avid Malignant Pleural Effusion in a Patient With Metastatic Adenoid Cystic Carcinoma and Concordance With 18F-FDG PET/CT.

ABSTRACT: Adenoid cystic carcinoma (ACC) is a rare cancer that arises from salivary glands and other secretory glands. Pulmonary metastases are frequently observed in ACC patients with metastatic disease. Previous research showed that ACC often shows high PSMA uptake on 68Ga-PSMA-11 PET/CT. Here, we present PET images from an ACC patient with pulmonal, pleural metastases, and malignant pleural effusion, with comparable tracer uptake on 68Ga-PSMA-11 PET and 18F-FDG PET.

A 59-year-old man with a history of adenoid cystic carcinoma (ACC) from the nasopharynx has previously been treated with surgery and postoperative radiotherapy. Eight years after the primary treatment, pulmonary metastases were diagnosed on a chest radiograph, which was performed because of a persisting cough. In a subgroup of patients with ACC disease, distant metastases can be detected several years after initial diagnosis, often related due to the indolent tumor growth of ACC and often asymptomatic metastases.[1,2] In case of recurrent or metastatic ACC disease, systemic therapy should mainly be considered for patients with symptomatic disease or rapid progression.[3,4] Although there is still no standard systemic treatment for ACC, previous single-arm phase 2 studies showed the efficacy of combinations of cytotoxic drugs[5] or a tyrosine kinase inhibitor.[6,7] Yet, response rates of these drugs are moderate, and participation in clinical trials is advised.[4] Previously, because of symptomatic disease, the patient received cabozantinib treatment in a clinical trial. Unfortunately, the clinical trial closed prematurely due to severe toxicity in other included patients, and the cabozantinib treatment was discontinued after 1 month.[8] After 1 year, his disease-related symptoms increased, and recently, the patient developed malignant pleural effusion (diagnosed on imaging, not validated with pleural puncture), without dyspnea. Therefore, other systemic treatment options were considered. Recently, this patient received both 68Ga-PSMA-11 PET and 18F-FDG PET imaging as part of the screening procedure for a 177Lu-PSMA radioligand therapy study. Because ACC tumors are often avid on 68Ga-PSMA PET/CT imaging[9] and PSMA radioligand therapy has shown good results in prostate cancer,[10,11] we initiated a clinical trial (NCT04291300) applying 177Lu-PSMA radioligand therapy for salivary gland cancer patients, including ACC patients. The time interval between the 68Ga-PSMA-11 PET and 18F-FDG PET scan was <1 week. In addition to a comparable uptake on both PET scans of the pulmonal and pleural metastases, the malignant pleural effusion was also clearly visible. PSMA PET imaging is most often performed in prostate cancer patients, yet malignant pleural effusion in prostate cancer is rare and only 1 case report on 68Ga-PSMA–avid malignant pleural effusion in prostate cancer has been reported.[12] PSMA PET imaging is lately being investigated for several cancers other than prostate cancer.[13] A, Image shows the MIP image of the 68Ga-PSMA-11 PET. B, Image shows the MIP image of the 18F-FDG PET.